Electrically-active materials are materials that respond to high electric fields and produce optical or mechanical effects. For example, electroluminescent devices include a phosphor layer (electrically-active material) that, when coupled to an electric field, can emit radiation, either directly or through an intermediate layer that absorbs the emitted energy and reemits it at a different wavelength. Typically, electroluminescent devices are made by depositing a conductive layer, which may be patterned, on a substrate, typically glass or a flexible polymer. An electrically-active material such as a phosphor can then be applied on top of the conductive layer. The layer, which contains the electrically-active layer, then is covered with a thin dielectric material to protect it from a transparent electrode which can be applied thereon. These types of devices, with two electrodes and an electrically-active layer sandwiched between them are capacitive devices and can store energy. It is critical with capacitive devices that the electric field created by one electrode can reach the other electrode in order to impart energy to the electrically-active layer. It is equally critical that there be no substantial conduction pathway between the two electrodes which would create a short-circuit and render the device inoperable.
Typically, dielectric or insulating materials are situated between the two plates in a capacitor or capacitive device. In order to support an electric field between the two plates, the dielectric needs to be very thin, have a high dielectric constant, or a combination of both. In some capacitive devices, inorganic materials having a very high dielectric constant have been employed as dielectric materials. For example, it is known to use barium titanate as a dielectric in electroluminescent devices. Non-conductive metal oxides such as aluminum oxide or titanium oxide can also be used as dielectrics in capacitive devices. Such inorganic dielectrics can be incorporated into capacitive device by vapor deposition techniques. Alternatively, composites can be formed by using a non-energy absorbing matrix or binder and including particles that have high dielectric constant therein. Since typical binders have relatively low dielectric constants, it is necessary to include a large volume of filler particles in the binder to get a high enough dielectric constant to support the electric field in the capacitive device.